In generators for power generating equipment, one or more windings are typically provided in a plurality of generally radially and axially extending, circumferentially spaced, slots. The windings are maintained within these slots by sets of wedges located partially in complementary surfaces adjacent the openings of the slots. The slots are disposed in the rotor and stator of the dynamoelectric machine. In the following description, the invention is described with respect to stator bars in stator slots, although it will be appreciated that the invention has like applicability to windings in the rotor slots.
Radial space in the stator slots is taken up by filler strips held in the slots between the wedges and the stator windings. As the generator ages, the materials will typically creep and shrink, tending to open up spaces between the stator bars, filler strips and wedges. In early machines of this type, flat filler strips were employed. However, in a short period of time, for example, within one or two years, the parts would become loose and it was necessary to remove the wedges, apply additional filler strips and re-wedge the machine. That process was oftentimes repeated.
Radial ripple springs have been previously used in order to progressively take up the clearance in the slots caused by creepage and shrinkage of the materials whereby a tight stator bar, filler strip and wedge arrangement may be maintained in the slot. When first installed, the radial ripple springs are compressed to about 80% of their full compression. As the various parts of the winding shrink, creep and settle, the springs expand and maintain radially opposed forces on the winding and wedges, respectively. Thus, radial ripple springs serve to provide follow-up forces where clearances would otherwise grow as the generator ages.
Because the current assembly procedures require the ripple springs to be compressed during the wedging process, the procedures are tedious and laborious. For example, it is first determined how much space there is between the wedges and stator bar. This is accomplished by disposing filler strips in the space. Once that dimension is determined, the filler strips are removed so that the ripple springs can be inserted in their stead. To insert the ripple springs into the machine, the springs are typically located between a pair of flat fillers. With these composite fillers and ripple springs disposed in the stator slots, the wedges are driven longitudinally along the slots, compressing the ripple springs. Currently, about 80% of the compressive force of the springs can be compressed by this wedging process, although the radial inward force on the stator wedges during installation makes it difficult to drive or displace the wedges longitudinally along the slot. Consequently, the more compression the spring is initially subjected to, the more difficult it is to drive the wedges. Further, efforts to drive the wedges to compress the springs to more than 80% of their full compression has resulted in radial forces so high that the material of the wedges will start to de-laminate. Thus, there is a practical limit to the degree of compression to which the ripple springs may be subjected during installation. Further, there is no readily suitable method for checking the spring compression when the assembly is complete.